As indicated by U.S. Pat. Nos. 8,048,002; 7,819,818; 7,708,700; and 7,384,399, it is possible to measure cognitive ability by utilizing eye tracking techniques and the gaze direction of the eye to be able to detect cognitive impairment. In order to detect cognitive impairment, accurate measurements must be made of the gaze direction of the eye as it tracks the dot.
The problem with simply presenting the dot on a computer screen is first and foremost that environmental effects such as ambient light and distractions disturb the test subject when the test subject is looking at the screen.
The second problem has to do with the exact position of the test subject's head with respect to the dots on the screen and more particularly with respect to the cameras that are utilized in the eye tracking procedure.
Thirdly, there is a problem in the eye tracking procedure with the positioning of an LED light source to present a precisely positioned glint on the surface of the retina in which the glint is used as a reference point when measuring the gaze angle.
The fourth problem is that if one seeks to measure head position with respect to the screen, cameras or LED sources, then a large error is introduced in the gaze angle measurement. As a result, accurate measurement of the direction of the eye as it tracks the dot is very difficult. For instance, one needs accuracy to the sub pixel level to obtain accurate gaze angle measurement. However, head error swamps this accuracy because head position is only available to accuracies of 5 to 10 pixels. What is now presented is additional general background.